Polycrystalline diamond (PCD) is a super-hard, also known as superabrasive material comprising a mass of inter-grown diamond grains and interstices between the diamond grains. PCD may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature. A material wholly or partly filling the interstices may be referred to as filler material. PCD may be formed in the presence of a sintering aid such as cobalt, which is capable of promoting the inter-growth of diamond grains. The sintering aid may be referred to as a solvent/catalyst material for diamond, owing to its function of dissolving diamond to some extent and catalyst its re-precipitation. A solvent/catalyst for diamond is understood be a material that is capable of promoting the growth of diamond or the direct diamond-to-diamond inter-growth between diamond grains at a pressure and temperature condition at which diamond is thermodynamically stable. Consequently the interstices within the sintered PCD product may be wholly or partially filled with residual solvent/catalyst material. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt solvent/catalyst for the PCD.
PCD may be used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. For example, PCD elements may be used as cutting elements on drill bits used for boring into the earth in the oil and gas drilling industry. In many of these applications the temperature of the PCD material may become elevated as it engages a rock formation, workpiece or body with high energy. Unfortunately, mechanical properties of PCD such as hardness and strength tend to deteriorate at high temperatures, largely as a result of residual solvent/catalyst material dispersed within it.
PCT patent publication number WO9929465 discusses that drilling hard rock and dealing with high well bore temperature gradients have been persistent problems in the drilling industry. The then current state-of-the-art TSP diamond cutter attachment procedure is to braze thermally stable polycrystalline diamond (TSP diamond) to carbide substrates. However, TSP brazing methods using TiCuSil alloy result in an undesirable discontinuous layer of TiC adjacent to the TSP diamond surface. Maximum strength properties are not realized unless a thin continuous layer of reaction product forms on the TSP surface (i.e. unless wetting is complete).
U.S. Pat. No. 7,377,341 discusses that a PCD body that is substantially free of the solvent catalyst material is precluded from subsequent attachment to a metallic substrate by brazing or other similar bonding operation. The attachment of such substrates to the PCD body is highly desired to provide a PCD compact element that can be readily adapted for use in many desirable applications. However, it is very difficult to bond the thermally stable PCD body to conventionally used substrates. Since conventionally formed thermally stable PCD bodies are devoid of a metallic substrate, they cannot be attached to a drill bit by conventional brazing process. Rather, the use of such a thermally stable PCD body in drilling application requires that the PCD body itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labour intensive, time consuming, and which does not provide a most secure method of attachment.
U.S. Pat. No. 7,435,377 discusses that polycrystalline diamond (PCD) and other ultra-hard materials may be joined to a supporting mass by means of brazing. However, a disadvantage of brazing is relates to concerns over potential heat damage of the PCD product, which has been a limiting factor in the past.
U.S. Pat. No. 7,487,849 discusses that because TSP (thermally stable product) is made by removing cobalt from a diamond layer, attachment of TSP to a substrate is significantly more complicated, as compared to the attachment of PDC to a substrate.
U.S. Pat. No. 7,533,740 discloses a cutting element comprising TSP material bonded to a tungsten carbide substrate by brazing (this patent uses the term “TSP” as described in U.S. Pat. Nos. 7,234,550 and 7,426,696, which use the term “TSP” to mean “thermally stable product”, including both partially and completely leached polycrystalline diamond compounds).
United States patent publication number 2008/0085407 discloses a super-abrasive compact element wherein a super-abrasive volume including a tungsten carbide layer may be brazed, soldered, welded (including frictional or inertial welding), or otherwise affixed to a substrate.
There is a need for PCD composite compact elements, particularly thermally stable PCD elements, having superior mechanical properties.